chore: fix login integration (#10318)

# Which Problems Are Solved

Login integration tests are not executed in the pipeline

# How the Problems Are Solved

The login integration tests are fixed and added as a pipeline workflow.
It  tests against the built login docker image.
On pipeline failures, developers are guided on how to fix them using a
dev container configured for this purpose.

# Additional Changes

- email domains are replaced by example.com. In case the tests were
accidentally run against a cloud instance, it wouldn't cause bounces.
- pnpm is upgraded, because the --filter argument doesn't work for the
install command on the old version.
- The login Dockerfile is optimized for docker image builds

# Additional Changes From Review for
https://github.com/zitadel/zitadel/pull/10305

These changes were requested from @peintnermax 

- The base dev container starts without any services besides the
database and the dev container itself
- CONTRIBUTING.md is restructured
- To reproduce pipeline checks, only the devcontainer CLI and Docker are
needed. This is described in the CONTRIBUTING.md
- The convenience npm script "generate" is added

# Additional Context

- Follow-up for PR https://github.com/zitadel/zitadel/pull/10305
- Base for https://github.com/zitadel/zitadel/issues/10277

package.json

@@ -1,15 +1,14 @@
 {
-  "packageManager": "pnpm@9.1.2+sha256.19c17528f9ca20bd442e4ca42f00f1b9808a9cb419383cd04ba32ef19322aba7",
+  "packageManager": "pnpm@10.13.1",
   "private": true,
   "name": "zitadel-monorepo",
   "scripts": {
+    "generate": "turbo run generate",
     "changeset": "changeset",
-    "devcontainer": "devcontainer",
-    "devcontainer:lint-unit": "pnpm devcontainer up --config .devcontainer/turbo-lint-unit/devcontainer.json --workspace-folder . --remove-existing-container",
-    "devcontainer:integration:login": "pnpm devcontainer up --config .devcontainer/login-integration/devcontainer.json --workspace-folder . --remove-existing-container",
+    "devcontainer:lint-unit": "FAIL_COMMANDS_ON_ERRORS=true devcontainer up --prebuild --config .devcontainer/turbo-lint-unit/devcontainer.json --workspace-folder .",
+    "devcontainer:integration:login": "FAIL_COMMANDS_ON_ERRORS=true devcontainer up --prebuild --config .devcontainer/login-integration/devcontainer.json --workspace-folder .",
     "clean": "turbo run clean",
-    "clean:all": "pnpm run clean && rm -rf .turbo node_modules",
-    "generate": "turbo run generate"
+    "clean:all": "pnpm run clean && rm -rf .turbo node_modules"
   },
   "pnpm": {
     "overrides": {
@@ -21,6 +20,7 @@
   "devDependencies": {
     "@changesets/cli": "^2.29.5",
     "@devcontainers/cli": "^0.80.0",
+    "sass": "^1.64.1",
     "turbo": "2.5.5"
   }
-}
+}